Nichia Corporation invented GaN-substrate blue light LED (light-emitting diode) in 1993, breaking through the technical bottleneck of blue light LED. The successful development of the high-brightness blue light LED in 1996 made it possible to combine yellow, green, and red phosphor powders into white light LED by stimulating the phosphors using blue light LED chips. Owing to the advantages such as high brightness, long life, and zero pollution, white light LED (also called semiconductor lighting source) is considered as a new-generation green lighting source, presenting a rapid development speed.
At present, white light LED is mainly used in lighting and display fields. In the display field, the display gamut is an important parameter for measuring the LED display device, i.e., the wider the display gamut is, and the richer the colors in the picture are. The LED backlight based LCD display has the advantages of good color reduction, low power consumption, long life and so on, occupying more than 90% of the LCD market. However, most display gamut of the currently used LED backlight based LCD display devices is about 70% NTSC (National Television Standards Committee), greatly reducing the viewing experience. The main reason is that the photochromic properties of the red phosphor powder used in the current white light LED have limitations in color purity, color coordinates and half width. As the viewing demand rises, wide color range LCD with the display gamut higher than 85NTSC % has gradually become one of the development trends in the LCD field. Since Mn4+ activated fluoride red phosphor powder has high excitation efficiency in the 460 nm blue light region, and can emit highly pure red light of which the mainly emitted light is at 630 nm, it can satisfactorily satisfy the requirements of the LED backlight devices in the wide color rang LCD.
Fluoride fluorescent material originates from the K2SiF6:Mn4+ fluoride fluorescent material reported by Paulusz of OS RAM from Germany in 1973. After the disclosure of white light LED in 1996, researchers had a new understanding about it. After 2006, the research of fluoride fluorescent materials gradually became the focus of scientific research and industrialization. LIU Ruxi synthesised a K2TiF6:Mn4+ red fluorescence material with the quantum efficiency (the ratio of the produced photons to all incident photons) up to 98% by replacing Mn4+ with some Ti4+ in K2TiF6 in the cation replacement method. Adachia's team synthesised a golden yellow K2SiF6:Mn4+ precipitation with an average particle size of about 80 μm by etching monocrystalline silicon for 10 minutes in a HF/KMnO4/H2O solution in the etching method. However, the fluoride phosphors that have been reported are irregular in morphology, low in quantum efficiency and poor in photochromic property, and cannot well meet the requirements of real white light LED phosphor powder, such as high luminous efficiency, uniform morphology and suitable particle size.